It's never a good idea to let the media just "SIT" in the tank.

The trapped sediments can harden, and become more difficult to remove ( clean ) later.

And some media can start clumping together, resulting in "channeling" of the media bed, and flow restriction through media bed.

Resulting in the need to replace all the media sooner than expected ( to restore proper flow ).

And since it's ONLY Water, it's not a big "expense" ( unlike using SALT in a Softener - needlessly ).

And another reason that METERED valves are not recommended for Filter applications is because there are NO Formulas for calculating how many gallons for the Setting of Frequency of backwashing.

With softener resin, there is a mathematical formula that is used.?